Secondary Structure and Location of a Magainin Analogue in Synthetic Phospholipid Bilayers

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Abstract
Magainins are cationic, membrane-active peptides which show broad-spectrum antimicrobial activity. We have investigated the secondary structure and location of an analogue of magainin 2 in synthetic phospholipid bilayers using a combination of Fourier transform infrared (FTIR) spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy. Ala19-magainin 2 amide exhibits both α-helix and β-sheet secondary structures in lipid bilayers containing either dipalmitoylphosphatidylglycerol (DPPG) or a 1:1 molar mixture of DPPG and dipalmitoylphosphatidylcholine (DPPC). The combination of FTIR and solid-state NMR results suggests that there are two populations of peptide. The secondary structure of one population is α-helix while that of the other population is β-sheet. We demonstrate that the solid-state NMR technique, rotational-echo double resonance (REDOR), can be used to measure both intra- and intermolecular dipole−dipole interactions in membrane-bound peptides. Our REDOR experiments indicate that α-helical Ala19-magainin 2 amide is bound near the phospholipid head groups.